1. Technical Field of the Invention
The present invention relates generally to a tool holding device for a percussion tool bit such as a cutter, a chisel, or a scoop used in, for example, electrically operated hammers, and more particularly to an improved structure of a tool holding device designed to provide for ease end safety of operations.
2. Background of Related Art
UK Patent Application GB-A-2 276 578 and UK Patent GB-B-2 276 579 disclose tool holding devices for use in electrically operated hammers. The tool holding devices include a tool bit carrier designed to hold a tool bit by engagement of locking members with grooves formed in the tool bit. The removal of the tool bit from the tool bit carrier is allowed by moving a front grip in an axial direction of the device to release the engagement of the locking members with the grooves of the tool bit.
The angular orientation of the tool bit relative to a body of the hammer is achieved by adjusting the angular position of the tool bit carrier relative to the body of the hammer since the angular relation between the tool bit and the tool bit carrier is fixed. The angular position of the tool bit carrier relative to the body of the hammer is held by engagement of steel balls mounted in a retainer sleeve connected to the body of the hammer with grooves formed in the tool bit carrier. The adjustment of the angular position of the tool bit carrier is achieved by moving a rear grip in the axial direction against a spring pressure to allow the engagement of the steel balls with the grooves to be released and turning the retainer sleeve to bring the steel balls into engagement with the other grooves.
The above conventional tool holding devices, however, have the following drawbacks.
The removal of the tool bit is, as described above, allowed by moving the front grip in the axial direction of the device to release the engagement of the locking members with the grooves of the tool bit, but the front grip may be moved accidentally to dislodge the tool bit by, for example, collision of the front grip with a work piece when the operator drills the work piece within a narrow work envelope or by the impact transmitted to the tool bit when the operator uses the hammer while holding the front grip.
Further, in order to adjust the angular position of the tool bit carrier relative to the body of the hammer, it is, as described above, necessary for the operator to take two actions, in sequence, of axially moving and turning the rear grip, but this Is quite inconvenience.